Python find all char in string

Find all occurrences of a substring in a string in Python

In this Python tutorial, we will learn how to find all occurrences of a substring in a string.

Table Of Contents

Find all occurrences of a substring using count()

The count() method is used to count the total occurrences of the given substring in a string. It takes three parameters.

string.count(substring,start,end)

Parameters
1. substring is the string to be counted
2. start is an optional parameter that takes an integer such that counting is started from the given index position.
3. end is an optional parameter that takes an integer such that counting is ended up to the given index position.

Frequently Asked:

It returns the number of occurrences of substring in from index positions start to end in the calling string object.

In this example, we will count the substring-“Python”.

# String string1="""Python programming language. Python is object-oriented, Python supports database connectivity and Python supports List,set, tuple and dictionary""" # Get the total number of occurrences - Python num = string1.count("Python") print(num)

We can see that “Python” occurred 4 times in the string.

In this example, we will count the substring-“Python” from a particular position.

# String string1="""Python programming language. Python is object-oriented, Python supports database connectivity and Python supports List,set, tuple and dictionary""" # Get the total number of occurrences - # Python from 1st position to 20th position num = string1.count("Python",0,19) print(num) # Get the total number of occurrences - # Python from 21st position to 65th position num = string1.count("Python",20,64) print(num)

We can see that “Python” occurred 1 time from the 1st position to the 20th position in the string and 2 times from the 21st position to the 65th position.

Find all occurrences of a substring using startswith()

The startswith() method is used to return the starting index of a particular substring. If we want to return all occurrence indices, we have to use list comprehension.

[iterator for iterator in range(len(string)) if string.startswith(substring, iterator)]

Parameters
1. substring is the string to be counted
2. iterator represents the position

To return the total number of occurrences, then we can apply the len() function to it.

len([iterator for iterator in range(len(string)) if string.startswith(substring, iterator)])

In this example, we will get the starting indices of the substring-“Python” and return the total number of occurrences.

# String string1="""Python programming language. Python is object-oriented, Python supports database connectivity and Python supports List,set, tuple and dictionary""" # Get the all indexpositions where substring "Python" exist in the string indices = [i for i in range(len(string1)) if string1.startswith("Python", i)] print(indices) # Get the total number of occurrences of "Python" num = len([i for i in range(len(string1)) if string1.startswith("Python", i)]) print(num)

We can see that “Python” occurred 4 times in the string and starting indices were also returned.

In this example, we will get the starting indices of the substring-“supports” and return the total number of occurrences.

# String string1="""Python programming language. Python is object-oriented, Python supports database connectivity and Python supports List,set, tuple and dictionary""" # Get the all indexpositions where substring "supports" exist in the string indices = [i for i in range(len(string1)) if string1.startswith("supports", i)] print(indices) # Get the total number of occurrences of "supports" num = len([i for i in range(len(string1)) if string1.startswith("supports", i)]) print(num)

We can see that “supports” occurred 2 times in the string and starting indices were also returned.

Find all occurrences of a substring using finditer()

The finditer() method is available in the re module which is used to return the starting index of a particular substring using the start() method. If we want to return all occurrence indices, we have to use list comprehension and iterate the string using an iterator.

[iterator.start() for iterator in re.finditer(substring, string)]

Parameters
1. substring is the string to be counted
2. string is the actual string

It returns a sequence a list of index positions where substring exists in the string. To return the total number of occurrences, then we can apply the len() function to it.

In this example, we will get the starting indices of the substring-“Python” and return the total number of occurrences.

import re # String string1="""Python programming language. Python is object-oriented, Python supports database connectivity and Python supports List,set, tuple and dictionary""" # Get the all indexpositions where substring "Python" exist in the string indices = [i.start() for i in re.finditer("Python", string1)] print(indices) # Get the total number of occurrences of "Python" num = len(indices) print(num)

We can see that “Python” occurred 4 times in the string and starting indices were also returned.

In this example, we will get the starting indices of the substring-“supports” and return the total number of occurrences.

import re # String string1="""Python programming language. Python is object-oriented, Python supports database connectivity and Python supports List,set, tuple and dictionary""" # Get the all indexpositions where substring "supports" exist in the string indices = [i.start() for i in re.finditer("supports", string1)] print(indices) # Get the total number of occurrences of "supports" num = len(indices) print(num)

We can see that “supports” occurred 2 times in the string and starting indices were also returned.

Summary

We have seen how to find and return the total number of occurrences of a particular substring using count(), startswith(), and finditer() methods. The startswith() and finditer() methods used list comprehension to return all the occurrences.

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Python How to Check If String Contains Characters from a List

To check if a Python string contains all the characters from a list, check if each character exists in the word:

chars = ["H", "e", "y"] word = "Hello" has_all = all([char in word for char in chars]) print(has_all)

To learn other useful string methods in Python, feel free to check this article.

Below you find a more detailed guide of how to check if a string contains characters from a list.

Step-by-step Guide

Given a list of characters and a string, you can check if all the characters of a list are found in the target string following these steps:

1. Loop through the list of characters.
2. Check if a character is in the target string.
3. Add the truth to a list.
4. Check if all truth values in a list are True.

Here is how it looks in code:

chars = ["H", "e", "y"] word = "Hello" truths = [] # 1. Loop through the chars for char in chars: # 2. Check if a character is in the target string truth = char in word # 3. Add the truth to a truths list truths.append(truth) # 4. Check if all boolean values are True has_all = True for truth in truths: has_all = has_all and truth print(has_all)

But you can make this piece of code shorter by using:

• List comprehension to shorten the 1st for loop.
• Built-in all() method to get rid of the 2nd loop. This method checks if all booleans are True.

This makes the code look the same as in the example solution in the introduction:

chars = ["H", "e", "y"] word = "Hello" has_all = all([char in word for char in chars]) print(has_all)

To be more general, you can implement a function that gets the job done.

Here is how it looks in code:

def has_all(chars, string): return all([char in string for char in chars]) # Example call print(has_all("Hello", ["H","i"]))

Conclusion

Today you learned how to check if a Python string contains all characters present in a list.

To recap, you need to run a loop through the list of the characters. Then you need to check if each of those characters exists in the target string.

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